The present invention relates to condensation heating facilities and, more particularly, to a system for regulating a blanket of secondary vapor in a vessel open to the atmosphere and containing a primary vapor shielded from the atmosphere by the secondary vapor.
Condensation heating facilities employing a secondary blanket of vapor to shield a primary blanket of vapor from the atmosphere are very well known to those skilled in the art. Two such systems are taught in U.S. Pat. No. 3,904,102 issued Sept. 9, 1975, to Tze Yao Chu, et al; and U.S. Pat. No. 3,947,240, issued Mar. 30, 1976, to Robert C. Pfahl, Jr. The cited patents teach maintenance of a secondary blanket by the continuous condensation of secondary vapor on an outer surface of a cooling coil, collection of the condensate in a trough from which it is drained off and reintroduced into a primary trough where it is boiled to reproduce secondary vapor. Compensation for loss of secondary vapors to the atmosphere is accomplished by feeding makeup secondary liquid from a reservoir to the primary trough via a line controlled by a control valve. The valve may be variously operated by sensors detecting a drop in the level of the top of the secondary vapor body or by sensors detecting changes in the secondary vapor concentration in the upper portion of the vessel. Such an arrangement while operating generally satisfactorily has been found to be difficult to control accurately resulting in oscillating periods of excessive and deficient secondary vapor within the vessel.
Another method of secondary vapor blanket control is taught by U.S. Pat. No. 4,055,217, issued Oct. 25, 1977, to Tze Yao Chu, et al; and its divisional U.S. Pat. No. 4,090,843, issued May 23, 1978, to the same inventors. In accordance with the cited patents, secondary vapor blanket control is achieved by condensing the secondary vapor on a cooling coil, collecting the condensate in a trough and siphoning the trough condensate into a reservoir containing secondary vapor liquid. The secondary liquid is then pumped from the storage tank through a line and onto a wick located in the body of secondary vapor and extending downward to a point proximate the primary vapor interface. As the secondary vapor liquid travels downward through the wick it is heated and vaporizes to form supplementary secondary vapor thus maintaining the vapor blanket. Such, an arrangement while operating generally satisfactorily requires an array of spray nozzels for even distribution of the secondary vapor liquid and working material located within the vapor phase heating vessel.